The present invention relates to an apparatus for cooling an electrical module arranged in a housing and, in particular, a base station of a mobile radio system or wireless subscriber line system.
In an electrically operated technical appliance, the lost power of components and modules through which current flows leads to a heating-up of the appliance. Since standard electrical components for technical appliances have only a limited admissible operating temperature range of, for example, up to 70xc2x0 C., they are cooled by cooling devices. These cooling devices are, for example, fans which establish an air flow in the housing, flowing around or through the electrical components and modules, and which consequently bring about a discharge of the thermal output produced.
During operation of the technical appliances outside enclosed spaces or in adverse conditions within enclosed spaces, adequate protection from environmental influences, such as, for example, dirt particles and liquids, must be additionally provided along with heat discharge. In this respect, protective regulations in accordance with the specified IP classes must be observed in order to ensure long-term functioning of the technical appliances.
It is known from DE 19755944 to provide in an air inlet of a housing a membrane filter for a superficial filtering of dirt particles from inflowing cooling air and for separating out liquids. In comparison with a housing known, for example, from DE 19626778, with an air/air heat exchanger, which ensures complete separation of an internal cooling circuit from an external cooling circuit, adequate protection of the electrical modules can be achieved for the aforementioned areas of use of the technical appliance with the corresponding protective regulations in a simple way by use of the membrane filter. At the same time, a temperature difference, required for the cooling, between the temperature of the ambient atmosphere and the temperature inside the housing is reduced.
A membrane filter of this type is based, for example, on a membrane known for use in articles of clothing by the designation Goretex, Sympatex, etc. This membrane includes a fine netting or knitted fabric of fibers, which permits a very small pore size. An example of a material which may be used for this is PTFE (polytetrafluoroethylene), also known by the name Teflon. The membrane is generally provided on a backing material, such as, for example, polyamide, in order to achieve a certain stability and resistance of the membrane filter.
The very small pore size of the membrane filter makes it more resistant to soiling in comparison with conventional filters, since, for example, dirt particles cannot become lodged in the knitted fabric of the membrane and are deposited on the surface of the filter. In spite of this property, dirt particles are deposited on the surface of the membrane filter and form what is known as a filter cake, which for the cooling air represents a resistance additionally to be overcome. This filter cake may have disadvantages with regard to minimizing the cooling air throughput due to the increased counterpressure with the resultant effect that the admissible temperature limit is exceeded.
The present invention is, therefore, directed toward specifying an arrangement for cooling an electrical module and a technical appliance which permits simple cleaning of the membrane filter.
The apparatus according to the present invention for cooling an electrical module arranged in a housing has at least one membrane filter, arranged in an air inlet of the housing in each case, for at least a superficial filtering of dirt particles from inflowing cooling air for cooling the electrical module and also at least one cooling device for establishing an air flow in the housing and for discharging the filtered cooling air, heated up from flowing through and/or around the module, out of the housing from at least one air outlet. The membrane filter is characterized by being associated with at least one vibration generator to undergo a mechanical vibration which causes the dirt particles deposited on the surface of the membrane filter to be dislodged.
The configuration of the apparatus according to the present invention has the advantage that the membrane filter is freed of the dirt particles deposited on the surface in a simple way by the mechanical vibration generated, in which the filter cake is virtually shaken off.
According to a first embodiment of the present invention, the membrane filter additionally separates out liquids at the surface, whereby use of the associated technical appliance is also possible outside enclosed spaces or under adverse ambient conditions.
According to a further embodiment of the present invention, the generated magnetic vibration has a frequency which corresponds to a natural resonant frequency of the membrane filter. This frequency brings about a mechanical movement of the membrane filter with a greatest possible amplitude, whereby more effective cleaning of the membrane filter is advantageously achieved.
According to four additional alternative embodiments, the vibration generator may be provided in the form of an electrodynamic transducer, an electromagnetic transducer, an electromechanical transducer or an electrostatic transducer.
In the case of the first three additional alternative embodiments, the membrane filter is mechanically coupled to an electromechanical, electromagnetic transducer, which generates mechanical vibrations. In this case, it is also possible, for example, for a frame in which the membrane filter is fastened to be made to undergo a mechanical vibration, it having to be ensured in any event that dirt particles or liquid cannot penetrate into the housing; for example, due to gaps or openings being produced by the vibration.
According to one embodiment, the electromechanical transducer may, for example, be provided in the form of a piezoelectric transducer.
In the case of the fourth additional alternative embodiment, the membrane filter is arranged between two capacitor plates, an electrostatic force between the capacitor plates bringing about the mechanical movement of the membrane filter. In this case, the membrane filter must be made entirely or partially from an electrically conductive material.
According to a development of the fourth additional alternative embodiment, the capacitor plates are provided in the form of an electrically conductive netting. This netting advantageously does not cause any restriction of the cooling air throughput and can be used both for electromagnetic shielding and for additional protection of the membrane filter from environmental influences.
According to a development referring back to the preceding embodiments, the membrane filter is made from an electrically conductive material as a capacitor plate, having the advantageous result of simplifying the mechanical construction.
According to a further embodiment of the present invention, a control device controls the vibration generator for the cleaning of the membrane filter periodically and/or on the basis of a degree of soiling of the membrane filter. The control device controls the vibration generator, for example, on the basis of a necessary rotational speed of the cooling device designed as a fan. In this case, the required cooling air throughput can be determined while taking into account the temperature difference between the outside atmosphere and the interior of the housing. If an increase in the speed of the fan by a certain factor is necessary to achieve the same cooling air throughput, or if the cooling air throughput at a constant speed of the fan falls below a certain threshold value, a certain degree of soiling of the membrane filter can be concluded and a cleaning operation initiated by the control device. Furthermore, a cleaning operation may be initiated by a pressure measurement in the interior of the housing; for example, under the control of a differential pressure switch. This involves permanently or periodically measuring the pressure in the housing and comparing it with a threshold value. If the measured pressure falls below this threshold value, the cleaning operation is initiated by the control device. In addition to these dynamic activations of the cleaning operation, the cleaning operation also may be performed periodically; for example, under the control of a timer in the control device. The cleaning of the membrane filter can, consequently, be freed of deposited dirt particles in a simple way outside the normal maintenance intervals of the technical appliance.
Furthermore, the control device may control, for example, the frequency of the vibration generated in the vibration generator.
The apparatus according to the present invention can be used in technical appliances with at least one electrical module, such as, for example, base stations of a mobile radio system or wireless subscriber line system (access network systems), traffic control devices, power supply devices or switch cabinets for a control system of industrial machines. In the same way, the apparatus according to the present invention can be used, for example, in smaller electrical appliances, such as, for example, a portable or stationary home computer, or in electrical measuring instruments.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures.